In the prototypical Single Diffusion Encoding (SDE; also known as Stejskal-Tanner or single Pulse Gradient Spin Echo) experiment, two RF pulses and two gradient pulses sensitise a sequence to molecular diffusion. A 90\(^{\circ }\)  RF storage pulse establishes a partial phase coherence in a system's spin precession in a strong magnetic field. A short gradient pulse dephases spins, and the system is permitted to evolve (and diffuse) for a period of time. During this evolution, a 180\(^{\circ }\)  refocusing RF pulse reverses the system's phase evolution. A final gradient pulse, identical to the first refocuses the system after another period passes, and readout can determine the spatial variation of magnetisation in the system [1]}.
